Piezo-electric frequency meter



Aug. 4, 1931. H. EBERHARD 1,817,030

\ PIEZQ ELECTRIC FREQUENCY METER Filed Nov. 2, 1926 W G: 620W 7 fl/JC/l/MEf flfV/Cf INVENTOR HEINRICH EBERHARD -with the accompanying drawing in Patented Aug. 4, 1931 UNITED STATES PATENT OFFICE nnmmcn EBEBHABD, OF BERLIN, GERMANY ASSIGNOR TO RADIO CORPORATION OF AMERICA, A CORPOBATIOH OF DELAWARE TWO-ELECTRIC FREQUENCY METER Application filed November 2,1826, Serial- No.

According to a suggestion of Professor Giebe itis possible to reveal or make perceptible by a luminous action the mechanica oscillations of natural periodcof piezoelectric crystals which are produced by high frequency electric oscillations. This method is very convenient in use and manipulation. However it is necessary to observe a certain amount of care for the reason that, if the electric stimulus is unduly intense, this is liable to occasion cracking of the quartz crystal. 7

Now, according to this invention the potential amplitude impressed on and applied to the oscillating crystal is automatically limited by that a glow-discharge lamp or some other means responsive to potential is dis osed in parallel to the said crystal. For instance, glow-discharge (or glim-) lamps with a filling of helium and neon, with a slight addition of Inercuryvapor, exhibit the property of responding to potentials below 100 volts which potentials cause them to flash up. With other gases and with special dispositions'of the electrodes, both substantially lower as well as high voltages at which the lamp will react, can be attained. Hence, the responding potential of the parallel-connected voltage-limit in means can be adjusted and adapted to fu fill the admissible or desirable conditions under which the crystal is to work quite ad libitum. A

The manner of carrying out this invention will readily be understood from the following description taken in connection which:

The single figure is a diagrammatic showing of a system embodying the invention.

If a glow-discharge lamp is used for the purpose before stated this allows of realizin an additional advantage; for, as shown in the figure the parallel combination of the oscillatin crystal K and the low-discharge lamp Iir is connected with t e terminals of a resonance or tuning circuit R which is excited from a transmitter. S, if the coupling, is first chosen rather tight, and if the circuit'R isv approximately set to resonanee, the glow-discharge lamp- G will found where t 145,865, and in Germany December 29, 1925.

first be caused to light up. This is a convenient sign and indication that the sender is tuned approximately to the correct wavethe coupling between S and R is loosened somewhat, and if the frequency of S is varled in very fine steps, a point will be e crystal K begins to oscillate and where it thus deprives the lamp G of energy. Arrangements may then be made 1n such a way that the lamp G becomes dark,

while the oscillating crystal K which, ac-

cording to Professor Giebe is confined within a rarefied air space (gas space), starts to luminesce instead. In this manner lamp G .afiords not only protection, but it acts at the. same time as a rough indicator of the resonance point.

In the event that several crystals K are I used, it is possible to employ a single glowdischarge lamp G as a safety device and as 'a rou h wave-length indicator for all of these di erent frequencies. The lamp G is most suitably disposed in close contiguity to the luminous tube in which the oscillating crystal is mounted so that both luminous actions can be conveniently observed simultaneously.

I claim as my invention: L 1. In combination, a first circuit, a tuned circuit including means to vary the tuning of the same, a glow discharge device connected in said tuned circuit and adapted to indicate the transfer of electrical energy from said first circuit to said tuned circuit as the tuning of said tuned circuit is varied, and means connected in said tuned circuit to indicate the condition. of resonance between said tuned circuit and the current flowing in said first circuit and simultaneously to render said indicating means inoperative. 2; In combination, a first circuit, a tuned circuit coupled thereto, means to vary the tunin of said last mentioned circuit, means to in icate the approximate condition of resonance between said tuned circuit and the current flowing in said first circuit, and means to indicate substantially the exact condition of resonance between said tuned circuit and the current flowing in said first circuit, said last mentioned means when functioning to indicate the condition of reeo nance serving also to render said first mentioned indicating means inoperative.

3. In combination, a first circuit, a tuned circuit coupled thereto, means to vary the tuning of said last mentioned circuit, a glow discharge device connected in said tuned circuit and adapted to indicate the transfer of electrical energy from said first circuit to said tuned circuit, and a iezoelectric resonator connected in paral el to said glow discharge device, said piezo-electric resonator having a natural period of vibration which will react upon the tuned circuit substantially only when the condition of resonance between said tuned circuit and the current fiowin in said first circuit is reached and where y said 'piezo-electric resonator renders the glow-discharge device inoperative substantially at resonance of said two circuits.

4. In combination, a primary circuit, a secondary circuit, means connected in said secondary circuit to indicate the transfer of ener from said primary to said secondary clrcuit when said circuits are tightly coupled, means to vary the coupling of said circuits, and a piezo-electric means to indicate the transfer of energy from said primary circuit to said secondary circuit when said circuits are loosely coupled together, said piezo-electric means reacting upon said first mentioned indicating means to render the same inactive when the natural period of vibration oi said piezo-electric means is substantially in resonance with the current flowing in said primary circuit.

5. In combination, a primary circuit, a secondary circuit, means connected in said secondary circuit to indicate 'ro hly the condition of resonance between sai circuits, and means to indicate substantially exactly the condition of resonance between said primary and said secondary circuits, said last mentioned means when indicati bengope rative to render said first mentioned in icatmg means inoperative.

ferred from said source to said circuit to deenergize said glow discharge device.

7. A wave meter comprising in combination, an alternating current circuit having a coupling coil, whereby said circuit may be coupled to a source of alternating current to tested a iezo-electric device having a predetermme natural period of vibration connected in said circuit, and a low discharge device connected across said device said glow discharge device being ener by the energy transferred from said source to said circuit, and said piezo-electric device reacting upon said circuit when the natural period of said device is in resonance with the frequency of energy transferred from said source to said circuit and said piezo-electric device reacting upon said glow discharge device at said condition of resonance to de-ener 'ze the same.

- HEIN ICH EBEBHARD.

6. A wave meter comprising in combination, an alternating current circuit having a coupling coil for coupling said circuit to the source of alternating current to be tested, a glow discharge device connected in said circuit, and a piano-electric device coupled to said circuit, said glow-lamp bein energized by energy transferred from said source to said circuit, said piezo-electrio device reacting upon said circuit when the natural period of said device is in resonance with the frequency of energy trans 

